1. Field of the Invention
The present invention relates to a system and method for calculating an optimum allowable transmission power level in an ad-hoc network communication path. More particularly, the present invention relates to a system and method for calculating an optimum transmission power level for transmission routes having a variable number of hops between nodes resulting in a maximum pipeline delay during transmission that does not exceed allowable levels for the service class provided.
2. Description of the Related Art
Ad-hoc networks have become a rapidly growing application in wireless mobile communications. An ad-hoc network is comprised of a number of mobile devices which are capable of direct and indirect communication with one another, such that each mobile device may be used as a router for data packet transmissions from other mobile devices. Transmitted data packets “hop” from mobile device to mobile device, creating a transmission path, until reaching a final destination. However, transmission paths between mobile devices are often subject to change as devices move, therefore ad-hoc network communication must be able to adapt and establish paths with optimum performance.
Typically, moving devices within an ad-hoc network result in variations in transmission path distance and associated transmission power levels. Although intelligent access points (IAPs) and stationary routers may theoretically include unlimited power supplies to provide transmission power, mobile devices are typically powered from rechargeable batteries. Therefore, a significant operation parameter in ad-hoc networks is the selection of transmission paths between devices requiring the lowest power consumption levels. Given no other factors, a transmission path comprised of short hops between multiple, closely spaced mobile devices will typically require less transmission power than a path comprised of fewer hops between widely spaced devices. Therefore a path requiring less transmission power is often possible where a large number of dispersed mobile devices within an ad-hoc network exist. Longer, direct transmission paths with fewer hops, as in the case occurring when an ad-hoc network has fewer dispersed mobile devices, will typically require greater transmission power levels. Therefore, a transmission path comprised of short hops between close mobile devices when possible, is the preferred communication route to conserve the limited power resources of mobile devices. However, a second factor beyond transmission path power consumption must be considered in ad-hoc communications networks.
As data packets are transmitted between multiple mobile devices, a cumulative transmission delay is created, which is not present in more direct transmission routes. Delays resulting from excessive hopping may be unsuitable for many service classes. For example, the “pipeline delays” resulting from excessive hopping is unsuitable for telephone communication, however certain data transfers may tolerate these larger delays. When the maximum accepted pipeline delay is small, the number of hops along the route between correspondents or between one correspondent and its IAP must be smaller than the number of hops along routes supporting unidirectional data transfer. As discussed above, transmission routes having a large number of hops require less transmission power, while routes having fewer hops, such as routes required for interactive voice data, use higher transmission powers. The resulting selected route in each case therefore, must satisfy pipeline delay requirements as well as address power consumption concerns for battery powered mobile devices.
Presently, routing schemes have included a number of methods. As described in U.S. Pat. No. 5,987,011 to Toh, which is incorporated herein by reference, conventional routing schemes are typically based on either broadcast or point-to-point routing. As discussed in Toh, numerous routing schemes have been implemented including cluster-based routing, destination sequence distance-vector routing and dynamic source routing. Each technique uses some combination of point-to-point and broadcast routing using the connection-oriented packet forwarding approach. Although each routing scheme provides a transmission path, no concern is given to the pipeline delay restrictions for differing service classes or the restricted power supplies of mobile devices. Excessive pipeline delays are often unacceptable for many service classes, however, transmission paths with lower delays typically require greater transmission power levels.
Accordingly, a need exists for a system and method in which maximum pipeline delays are determined for service classes in an ad-hoc network, and an optimum transmission power level calculated for a selected transmission path satisfying these delay requirements.